Vacuum pump provided with vibration damper

ABSTRACT

A vacuum pump assembly is provided with a vacuum pump and external unit coupled by a vibration damper. The vibration damper comprises a plurality of piezoelectric actuators and a plurality of sensors. Actuators attenuate vibration propagated from the pump to the external unit to which the pump is connected and/or vice versa, while the sensors are capable of providing a measure of the vibrations to controlling said actuators.

FIELD OF THE INVENTION

The present invention relates to a vacuum pump, which is provided with a vibration damper.

More particularly, the present invention relates to a turbomolecular vacuum pump provided with a damper attenuating the propagation of vibrations induced by the rotation of the pump rotor to an external unit to which the pump is connected. The external unit may be a chamber in which it is desired to create vacuum conditions.

BACKGROUND OF THE INVENTION

Several conventional applications utilising the vacuum chamber with a vacuum pump attached thereto are particularly sensible to the mechanical vibrations inevitably generated by the rotation of the pump's rotor. The electron microscopes and the systems for measuring and repairing the masks for manufacturing integrated electronic circuits may serve as examples of such applications.

In order to reduce the transmission of mechanical stresses from the pump to the vacuum chamber, some manufacturers have replaced the conventional mechanical bearings with magnetic bearings or suspensions. However, the use of magnetic suspensions does not always allow for damping the pump-generated vibrations down to the desirable levels.

Moreover, turbomolecular pumps customary used in the applications demanding high degrees of vacuum, do not discharge directly to the external environment, but they are connected to a forepump. Thus, it is necessary to consider the vibrations generated by forepump and transmitted to the vacuum pump and from the latter to the vacuum chamber.

For reasons mentioned above, the vacuum pump is often equipped with a vibration damper disposed between the pump and the vacuum chamber.

According to the prior art, and referring to FIG. 1, a vacuum pump 100 has an inlet port 110, a discharge port 120 and gas pumping means 130 that, in case of turbomolecular pumps, consists of a set of pumping stages, each comprising a rotor disc co-operating with a corresponding stator ring. An example of a turbomolecular pump is disclosed in the U.S. Pat. No. 5,387,079. A flange 115 is provided in correspondence with the inlet port 110 for coupling with flange 210 of chamber 200 where vacuum conditions are to be created. A similar flange 125 is provided in correspondence with discharge port 120 for coupling with a forepump 300, generally through a flanged bellows 400. According to the prior art, vibration dampers 140 are, for instance, connected between the pump 100 and the chamber 200. They essentially comprise a first flange 150 coupled with flange 115 of pump 100, a second flange 160 coupled with flange 210 of vacuum chamber 200, a flexible steel bellows 170 ensuring vacuum tightness, and a plurality of rubber members 180 (three in the embodiment shown in FIG. 1), uniformly spaced around bellows 170 along the circumferences of flanges 150, 160 and ensuring damping of the mechanical vibrations transmitted by pump 100.

Rings 190, 290 are provided between the flanges to allow centring O-rings 195, 295 intended to ensure vacuum tightness between the flanges.

A similar damper could also be used downstream vacuum pump 100 and be connected between flange 125 of the discharge port of the pump and flange 310 of the inlet port of forepump 300.

It is clear that rubber members 180 used according to the prior art form a passive damper, which attenuates vibration propagation from the pump to the vacuum chamber only in part and in small frequency ranges.

It is a main object of the present invention to provide a vacuum pump equipped with a mechanical vibration damper having improved characteristics.

It is another object of the present invention to provide a vacuum pump equipped with a small-size, reliable and inexpensive damper.

The above and other objects are achieved by a vacuum pump as claimed in the appended claims.

SUMMARY OF THE INVENTION

Advantageously, the vacuum pump according to the invention comprises a damper utilising piezoelectric actuators.

Piezoelectric devices are devices that, when fed with an appropriate voltage, are capable of generating a force which intensity depends on the applied voltage and therefore is controllable. Conversely, these devices can be used to generate a voltage signal proportional to a possible applied force.

By using piezoelectric actuators it is therefore possible to control the actuators so that they impart a vibration of substantially the same amplitude as that measured onboard the vacuum pump but in phase opposite thereto, whereby a substantially null resulting vibration is obtained.

According to an embodiment of the present invention, said piezoelectric actuators are arranged around the metal bellows, in place of the conventional rubber members.

According to another embodiment, said piezoelectric actuators may be directly mounted on the flange of the inlet and/or discharge port of the vacuum pump, around the centring ring and the O-ring, so that the metal bellows and the related flanges can be dispensed with, thereby reducing the axial size of the pump-damper assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the vacuum pump according to the invention, given by way of non limiting example, will be described in more detail hereinafter, with reference to the accompanying drawings, in which:

FIG. 1 is a longitudinal sectional view of a vacuum pump equipped a damper according to the prior art.

FIG. 2 is a longitudinal sectional view of a damper according to a first embodiment of the invention;

FIG. 3 a is a block diagram of a first embodiment of a control logic arrangement for the damper;

FIG. 3 b is a block diagram of a second embodiment of a control logic arrangement for the damper;

FIG. 4 a is a block diagram of a third embodiment of a control logic arrangement for the damper;

FIG. 4 b is a block diagram of a fourth embodiment of a control logic arrangement for the damper;

FIG. 5 a is a partial cross-sectional view of the damper according to a second embodiment of the invention;

FIG. 5 b is a partial cross-sectional view of a detail of the damper of FIG. 5 a;

FIG. 6 a is a plan view of the damper according to a third embodiment of the invention;

FIG. 6 b is a cross-sectional view, taken along line B-B, of the damper of FIG. 6 a;

FIG. 6 c is a cross-sectional view, taken along line C-C, of the damper of FIG. 6 a;

FIG. 6 d is a cross-sectional view, taken along line B-B, of the damper of FIG. 6 a;

FIG. 7 a is a plan view of the damper according to a fourth embodiment of the invention;

FIG. 7 b is a cross-sectional view, taken along line B-B, of the damper of FIG. 7 a;

FIG. 8 a is a plan view of the damper according to a fifth embodiment of the invention;

FIG. 8 b is a cross-sectional view taken along line B-B, of the damper of FIG. 8 a.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 2, there is shown a vibration damper 14 according to the present invention, which is mounted, by means of corresponding flanges 150, 160, between a vacuum pump 100 and a chamber 200 where vacuum is to be created.

Damper 14 further comprises a vacuum-tight steel bellows 170 arranged between flanges 150, 160. Piezoelectric actuators A_(i), which in this embodiment made of parallelepiped or cylindrical blocks 18, are arranged around bellows. Preferably the piezoelectric actuators A_(i) are uniformly arranged around bellows 170: for instance, three actuators, spaced apart by 120°, are provided.

The actuators A_(i) are actively controlled through a driving signal capable of generating vibrations substantially equal and opposite to the vibrations, which are produced onboard the vacuum pump and are measured by corresponding sensors, and which are not to be transmitted to vacuum chamber 200.

Referring to FIG. 3 a, a first embodiment of the control logic circuitry of actuators A_(i) is disclosed in which an independent closed-loop control system is provided for each sensor-actuator pair. Each control system includes a single-variable regulator R_(i), implemented in analogue or digital technology, which receives from a corresponding sensor S_(i), for instance an accelerometer, the value of the corresponding acceleration measured at the pump. Depending on such value, regulator R_(i) determines the suitable signal to be sent to driver D_(i) acting upon the corresponding piezoelectric actuator A_(i). It is possible that the control signals from regulator R_(i) may also depend on external quantities E_(i) different from those measured by sensors S_(i).

The external quantities E_(i) may represent the external disturbances acting on the system, and measurement thereof may serve to implement an open-loop feed-forward control. A corresponding implementing diagram of the control logic of actuators A_(i), shown in FIG. 3 b, allows for compensating the external disturbances before they affect the vibrations. Such a result can be obtained by implementing inside the regulator an accurate mathematical model capable of predicting the effects of the disturbances on the mechanical system.

Generally the same piezoelectric actuators A_(i) are capable of acting as sensors for detecting an acceleration: thus, other piezoelectric members, with the same structure as the actuators but acting as vibration sensors, can be used in place of the usual accelerometers. By uniformly distributing a sufficient number of piezoelectric members A_(i) along the circumferences of flanges 150, 160, the even-position members could for instance be used as actuators and the odd-position members as drivers.

Of course, also in case when actual accelerometers are used, it will be convenient to uniformly arrange a sufficient number of said accelerometers along the circumferences of the flanges 150, 160, by alternating the accelerometers with the piezoelectric actuators A_(i).

The regulators R_(i) can possibly act more effectively if vibration detection is carried out at the point where the actuator force is applied: in such case, sensors and actuators may be located as close as possible to one another, as it is disclosed in more details below.

Referring to FIG. 4 a, a third embodiment of the control logic circuitry of actuators A_(i) is disclosed. According to this embodiment a plurality of vibration sensors S₁ . . . S_(n) mounted onboard pump 100, a plurality of drivers D₁ . . . D_(n) capable of controlling piezoelectric actuators A_(i) . . . A_(n), and a multi-variable regulator R are provided.

The regulator R, implemented in analogue or digital technology, receives the signals representative of the vibrations from the vacuum pump, through sensors S₁ . . . S_(n). Depending on such signals, regulator R determines the control signals to be fed to drivers D₁ . . . D_(n) acting on piezoelectric actuators A_(i) . . . A_(n). The actuators generate a vibration that depends on the signal sent by regulator R, the signal being chosen so that the vibration produced is substantially equal and opposite to that measured by the sensors S₁ . . . S_(n).

Also in this case, the control logic is a closed-loop logic. Moreover, it is possible to make such control signals depend also on other quantities E measured at the pump.

Similarly to what disclosed above in connection with the single-variable regulators R_(i), an implementing diagram of the control logic of actuators A_(i) providing for an open-loop feed-forward control, as shown in FIG. 4 b, may be envisaged also when a multi-variable regulator R is used.

Regulator R is a multi-variable regulator, in which the control law for drivers D_(i) is the same for all actuators A_(i) and depends on the signals coming from all sensors S_(i).

In the alternative, regulator R might be implemented as a cascade of as many single-variable regulators R_(i) as the sensor-actuator pairs are, and of a final multi-variable synthesis block.

It is to be appreciated that number of sensors S_(i) may not be equal to the number of piezoelectric actuators A_(i), even though it is convenient to use the same number of sensors S_(i) and actuators A_(i) for constructive reasons.

Due to the optimum performance attainable by the control systems described above, piezoelectric actuators of a small size (i.e. much smaller than those of the conventional rubber members) can be used to dampen the vibrations measured on the vacuum pump. Thus, it is possible to have embodiments according to the present invention having a reduced axial size of the vacuum pump and its damper. Moreover, these embodiments could allow for improving the pumping characteristics of the pump-damper assembly, by reducing the flow resistance.

FIG. 5 a shows part of a damper 24 of a vacuum pump according to a second embodiment of the invention.

In this embodiment, flange 115 of the vacuum pump inlet port is directly coupled with counterflange 210 of a vacuum chamber through securing screws 20 uniformly distributed along the circumference of said flange 115, around centring ring 190 and the corresponding O-ring 195, and through corresponding securing nuts 21.

Piezoelectric actuators A_(i) are formed by cylindrical washers 28 mounted around stems 20 a of securing screws 20, in contact with flange 115 on the one side and with counterflange 210 on the other side. Thus, the axial thrust (shown by arrows F₂) of actuators 28 can be effective on the one side on the pump and on the other side on the vacuum chamber, thereby compensating for the axial vibrations measured onboard the pump and resulting in a reduction of the transmitted vibration.

In this second embodiment metal bellows 170 and the corresponding flanges 150, 160 can therefore be dispensed with, a consequent reduction of the axial size of the pump-damper assembly.

Also in this second embodiment the vibrations can be measured by accelerometers mounted onboard the pump. Similarly to the preceding embodiment, damper 24 may comprise a plurality of piezoelectric members A_(i) used as sensors. Also these sensors preferably consist of washers arranged around stems 20 a of securing screws and alternating with the piezoelectric actuators along the circumference of damper 24.

FIGS. 6 a to 6 c show a third embodiment of the invention. According to the third embodiment, piezoelectric actuators A_(i) are formed by parallelepiped or cylindrical blocks 38. They are mounted between a pair of circular supports 116, 211, directly located between flange 115 of the vacuum pump inlet port and counterflange 210 of a vacuum chamber, around centring ring 190 and the corresponding O-ring 195 ensuring vacuum tightness, similarly to the embodiment shown in FIG. 5 a.

Preferably, support 116 comprises suitable seats 116 receiving said actuators 38. As shown by arrow F₃ in FIG. 6 b, due to such an arrangement, the axial thrust of piezoelectric actuators 38 can be directly transmitted to the vacuum pump and the vacuum chamber through respective flanges 115, 210, whereby a substantially null resulting vibration is obtained.

In this embodiment also the metal bellows and the corresponding flanges are eliminated, with a substantial reduction of the overall axial size of the pump-damper assembly.

Even though the vibrations can be detected by accelerometers mounted on the vacuum pump, FIG. 6 a shows an alternative solution, already mentioned hereinbefore, in which damper 34 comprises piezoelectric sensors 39. The sensors consist of piezoelectric parallelepiped or cylindrical plates, of the same kind as used for actuators 38, and are arranged along the circumference of support 116 alternated with actuators 38.

In the embodiments disclosed above, piezoelectric actuators A_(i) are mounted so as to attenuate transmission of axial vibrations from vacuum pump 100 to vacuum chamber 200.

FIGS. 7 a and 7 b show a fourth embodiment of the invention, where a damper 44 according to the invention comprises piezoelectric actuators A_(i), consisting of parallelepiped or cylindrical plates 48, which can be used to prevent transmission of radial vibrations.

In that embodiment, piezoelectric actuators 48 are mounted between a pair of circular supports 117, 212 located between flange 115 and counterflange 210, so that they can exert a radial thrust on flanges 115, 210 (as shown by arrows F₄ in FIG. 7 b).

FIGS. 8 a, 8 b show a pump arrangement according to a fifth embodiment of the invention, comprising first and second piezoelectric actuators 581, 582 capable of dampening axial vibrations and radial vibrations, respectively (as shown by arrows F₅₁, F₅₂ in FIG. 8 b).

The first and second piezoelectric actuators 581, 582 can exert an axial thrust and a radial thrust, respectively, on the vacuum pump and the vacuum chamber connected to the pump. The vacuum chamber is connected through flange 210 to a support 213 shaped so as to have a pair of mutually orthogonal walls facing corresponding orthogonal walls of a corresponding support 118 connected to flange 115 of the vacuum pump.

Thus, piezoelectric actuators 581, 582 can be mounted as follows. The first actuators 581 are in contact at their bottom ends with support 118 connected to the vacuum pump, and their top ends with support 213 are connected to flange 210 of the vacuum chamber. Therefore the first actuators 581 are capable of transmitting an axial thrust. The second actuators 582 are in contact at their inner sides with support 118 connected to flange 115 of the vacuum pump and at their outer sides with support 213 connected to flange 210 of the vacuum chamber, whereby they are capable of transmitting a radial thrust.

The first and second actuators 581, 582 consist of piezoelectric parallelepiped or cylindrical plates uniformly arranged along the circumference of flange 115.

In this embodiment also the pump vibrations can be detected by accelerometers mounted on the pump. In the alternative, damper 54 may comprise first and second piezoelectric members A_(i) used as sensors to detect axial vibrations and radial vibrations, respectively.

In yet another embodiment of the invention, instead of alternating piezoelectric actuators and sensors along the circumference of vacuum pump flange 115, integrated pairs of piezoelectric members are used, wherein one member acting as a sensor and the other as an actuator.

An example of such embodiment is shown in FIG. 6 d, with reference to a damper of the kind shown in FIGS. 6 a to 6 c.

A piezoelectric sensor 39′ and a piezoelectric actuator 38′, separated by a plate 37, are received in each seat 115 a formed in flange 115. Arrows F₃′, F₃″ denote the operational directions of the sensor and the actuator, respectively, which are therefore coaxially mounted.

FIG. 5 b shows an arrangement relevant to the second embodiment of the invention shown in FIG. 5 a. A piezoelectric sensor 28′ and a piezoelectric actuator 29′, both consisting of a washer, are stacked on stem 20 a of each screw 20 and are separated by a washer 37. Arrows F₂′, F₂″ denote the operational directions of said sensor and actuator, respectively, which are therefore coaxially mounted.

It is clear that this embodiment of the invention provides considerable advantages in terms of accuracy in vibration damping, since the actuator preventing transmission of vibrations is located exactly at the same position where the vibrations are detected.

Though the above description refers to a vacuum pump equipped with a damper located at the input port, in order to attenuate vibrations transmitted from the vacuum pump to a vacuum chamber, a similar damper could be for instance located also at the discharge port, to attenuate vibration transmission from the forepump to said vacuum pump or between the pump and other external units. 

1. A vacuum pump assembly comprising: an external unit; a vacuum pump(100) which provides vacuum within the external unit, said pump comprising a body with an inlet port (110), a discharge port (120) and means (130) for pumping a gas from said inlet port to said discharge port; and a vibration damper (14; 24; 34; 44; 54) attenuating vibration transmission between the body of said pump and the external unit, said vibration damper comprising at least one piezoelectric actuator (A_(i)).
 2. The vacuum pump assembly as claimed in any claim 1, wherein said pump is a turbomolecular pump.
 3. The vacuum pump assembly as claimed in claim 2, further comprising a sensor (S_(i)) controlling said at-least one piezoelectric actuator (A_(i)).
 4. The vacuum pump assembly as claimed in claim 3, wherein said vibration damper (14; 24; 34; 44; 54) is positioned in correspondence with at least one of said input and discharge ports (110, 120).
 5. The vacuum pump assembly as claimed in claim 4, wherein said vibration damper further comprises a vacuum-tight bellows (17) equipped at its ends with a first and a second flanges (150, 160), said first flange and said second flange are coupling said vibration damper to said pump and the external unit, respectively.
 6. The vacuum pump assembly as claimed in claim 5, wherein said vibration damper (14) comprises a plurality of sensors (S₁ . . . S_(n)) and a plurality of piezoelectric actuators (A₁ . . . A_(m))(18), wherein said actuators, preferably of parallelepiped or cylindrical shape, are uniformly distributed around said bellows (17) between said first flange and said second flange.
 7. The vacuum pump assembly as claimed in claim 3, wherein said sensor is a piezoelectric sensor.
 8. The vacuum pump assembly as claimed in claims 6, wherein said sensors are uniformly distributed around said bellows.
 9. The vacuum pump assembly as claimed in claim 4, wherein said actuators are formed by washers mounted around securing screws (20) affixing the pump and the external unit.
 10. The vacuum pump assembly as claimed in claim 7, wherein at least one of said piezoelectric actuators is coaxially mounted relative to at least one of said piezoelectric sensors.
 11. The vacuum pump assembly as claimed in claim 2, wherein said vibration damper comprises a first and a second piezoelectric actuators (581, 582) damping vibrations in two mutually perpendicular directions.
 12. The vacuum pump assembly as claimed in claim 11, wherein said vacuum pump (100) is a rotary pump and one of said mutually perpendicular directions corresponds with a rotation axis of said vacuum pump.
 13. The vacuum pump assembly as claimed in claim 3, further comprising a control system having at least one regulator (R; R_(i)) controlling one or more of said piezoelectric actuators (A₁ . . . A_(m)), depending on the signals from said sensors (S₁ . . . S_(n)).
 14. The vacuum pump assembly as claimed in claim 2, further comprising a control system having at least one regulator (R; R_(i)) controlling one or more of said piezoelectric actuators (A₁ . . . A_(m)) based on the value of external quantities (E₁ . . . E_(m)) representative of the external disturbances imposed on said pump. 